Systems and methods for mitigating avalanche photodiode (apd) blinding

ABSTRACT

Described herein are systems and methods that that mitigate avalanche photodiode (APD) blinding and allow for improved accuracy in the detection of a multi-return light signal. A blinding spot may occur due to saturation of a primary APD. The systems and methods include the incorporation of a redundant APD and the utilization of time diversity and space diversity. Detection by the APDs is activated by a bias signal. The redundant APD receives a time delayed bias signal compared to the primary APD. Additionally, the redundant APD is positioned off the main focal plane in order to attenuate an output of the redundant APD. With attenuation, the redundant APD may not saturate and may have a successful detection during the blinding spot of the primary APD. Embodiments may include multiple primary APDs and multiple secondary APDs.

BACKGROUND A. Technical Field

The present disclosure relates generally to systems and methods foravalanche photodiode (APD), and more particularly for APDs utilized inlight detection applications such a light detection and ranging system(LIDAR).

B. Background

In a light detection and ranging system, such as a LIDAR system,multiple peaks in a return signal may be received in close timeproximity of one another. Since the photodiodes of the LIDAR systems maysaturate and exhibit reverse bias avalanche recovery phenomena, ablinding spot may occur in the APD detection. The blinding spot maylimit the ability of the LIDAR system to detect peaks in themulti-return light signal. In this situation the APD may be insensitiveto light and unable to detect a peak in the multi-return light signaluntil the APD has recovered from saturation.

Accordingly, what is needed are systems and methods that mitigate APDblinding and allow for accurate detection of multi-return light signals.

BRIEF DESCRIPTION OF THE DRAWINGS

References will be made to embodiments of the invention, examples ofwhich may be illustrated in the accompanying figures. These figures areintended to be illustrative, not limiting. Although the invention isgenerally described in the context of these embodiments, it should beunderstood that it is not intended to limit the scope of the inventionto these particular embodiments. Items in the figures are not to scale.

FIG. 1 depicts the operation of a light detection and ranging systemaccording to embodiments of the present document.

FIG. 2 illustrates the operation of a light detection and ranging systemand multi-return light signals according to embodiments of the presentdocument.

FIG. 3 depicts a LIDAR system with a rotating mirror according toembodiments of the present document.

FIG. 4A graphically illustrates the current-voltage characteristics of aphotodiode according to embodiments of the present document.

FIG. 4B graphically illustrates the size on a blinding spot according toembodiments of the present document.

FIG. 5 graphically illustrates a detected multi-return light signalcomprising a blinding spot according to embodiments of the presentdocument.

FIG. 6 depicts a light detector with a redundant APD according toembodiments of the present document.

FIGS. 7A, 7B, 7C graphically illustrates waveforms for the operation ofthe light detector with a redundant APD according to embodiments of thepresent document.

FIG. 8 depicts a flowchart for detecting multi-return light signalsutilizing a light detector with a redundant APD according to embodimentsof the present document.

FIG. 9 depicts a simplified block diagram of a computingdevice/information handling system according to embodiments of thepresent document.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description, for purposes of explanation, specificdetails are set forth in order to provide an understanding of theinvention. It will be apparent, however, to one skilled in the art thatthe invention can be practiced without these details. Furthermore, oneskilled in the art will recognize that embodiments of the presentinvention, described below, may be implemented in a variety of ways,such as a process, an apparatus, a system, a device, or a method on atangible computer-readable medium.

Components, or modules, shown in diagrams are illustrative of exemplaryembodiments of the invention and are meant to avoid obscuring theinvention. It shall also be understood that throughout this discussionthat components may be described as separate functional units, which maycomprise sub-units, but those skilled in the art will recognize thatvarious components, or portions thereof, may be divided into separatecomponents or may be integrated together, including integrated within asingle system or component. It should be noted that functions oroperations discussed herein may be implemented as components. Componentsmay be implemented in software, hardware, or a combination thereof.

Furthermore, connections between components or systems within thefigures are not intended to be limited to direct connections. Rather,data between these components may be modified, re-formatted, orotherwise changed by intermediary components. Also, additional or fewerconnections may be used. It shall also be noted that the terms“coupled,” “connected,” or “communicatively coupled” shall be understoodto include direct connections, indirect connections through one or moreintermediary devices, and wireless connections.

Reference in the specification to “one embodiment,” “preferredembodiment,” “an embodiment,” or “embodiments” means that a particularfeature, structure, characteristic, or function described in connectionwith the embodiment is included in at least one embodiment of theinvention and may be in more than one embodiment. Also, the appearancesof the above-noted phrases in various places in the specification arenot necessarily all referring to the same embodiment or embodiments.

The use of certain terms in various places in the specification is forillustration and should not be construed as limiting. A service,function, or resource is not limited to a single service, function, orresource; usage of these terms may refer to a grouping of relatedservices, functions, or resources, which may be distributed oraggregated.

The terms “include,” “including,” “comprise,” and “comprising” shall beunderstood to be open terms and any lists the follow are examples andnot meant to be limited to the listed items. Any headings used hereinare for organizational purposes only and shall not be used to limit thescope of the description or the claims. Each reference mentioned in thispatent document is incorporate by reference herein in its entirety.

Furthermore, one skilled in the art shall recognize that: (1) certainsteps may optionally be performed; (2) steps may not be limited to thespecific order set forth herein; (3) certain steps may be performed indifferent orders; and (4) certain steps may be done concurrently.

A. Light Detection and Ranging System

A light detection and ranging system, such as a LIDAR system, may be atool to measure the shape and contour of the environment surrounding thesystem. LIDAR systems may be applied to numerous applications includingboth autonomous navigation and aerial mapping of a surface. LIDARsystems emit a light pulse that is subsequently reflected off an objectwithin the environment in which a system operates. The object may beconsidered a “reflector” The time each pulse travels from being emittedto being received may be measured (i.e., time-of-flight “TOF”) todetermine the distance between the object and the LIDAR system. Thescience is based on the physics of light and optics.

In a LIDAR system, light may be emitted from a rapidly firing laser.Laser light travels through a medium and reflects off points of thingsin the environment like buildings, tree branches and vehicles. Thereflected light energy returns to a LIDAR receiver (detector) where itis recorded and used to map the environment.

FIG. 1 depicts operation 100 of a light detection and ranging components102 and data analysis & interpretation 109 according to embodiments ofthe present document. Light detection and ranging components 102 maycomprise a transmitter 104 that transmits emitted light signal 110,receiver 106 comprising a detector, and system control and dataacquisition 108. Emitted light signal 110 propagates through a mediumand reflects off object 112. Return light signal 114 propagates throughthe medium and is received by receiver 106. System control and dataacquisition 108 may control the light emission by transmitter 104 andthe data acquisition may record the return light signal 114 detected byreceiver 106. Data analysis & interpretation 109 may receive an outputvia connection 116 from system control and data acquisition 108 andperform data analysis functions. Connection 116 may be implemented witha contact or non-contact communication method. Transmitter 104 andreceiver 106 may include an optical lens (not shown). Transmitter 104may emit a laser beam having a plurality of pulses in a particularsequence. In some embodiments, light detection and ranging components102 and data analysis & interpretation 109 comprise a LIDAR system.

FIG. 2 illustrates the operation 200 of light detection and rangingsystem 202 including multi-return light signals: (1) return signal 203and (2) return signal 205 according to embodiments of the presentdocument. Light detection and ranging system 202 may be a LIDAR system.Due to the laser's beam divergence, a single laser firing often hitsmultiple objects producing multiple returns. The light detection andranging system 202 may analyze multiple returns and may report eitherthe strongest return, the last return, or both returns. Per FIG. 2,light detection and ranging system 202 emits a laser in the direction ofnear wall 204 and far wall 208. As illustrated, the majority of the beamhits the near wall 204 at area 206 resulting in return signal 203, andanother portion of the beam hits the far wall 208 at area 210 resultingin return signal 205. Return signal 203 may have a shorter TOF and astronger received signal strength compared with return signal 205. Lightdetection and ranging system 202 may record both returns only if thedistance between the two objects is greater than minimum distance. Inboth single and multi-return LIDAR systems, it is important that thereturn signal is accurately associated with the transmitted light signalso that an accurate TOF is calculated.

Some embodiments of a LIDAR system may capture distance data in a 2-D(i.e. single plane) point cloud manner. These LIDAR systems may be oftenused in industrial applications and may be often repurposed forsurveying, mapping, autonomous navigation, and other uses. Someembodiments of these devices rely on the use of a single laseremitter/detector pair combined with some type of moving mirror to effectscanning across at least one plane. This mirror not only reflects theemitted light from the diode, but may also reflect the return light tothe detector. Use of a rotating mirror in this application may be ameans to achieving 90-180-360 degrees of azimuth view while simplifyingboth the system design and manufacturability.

FIG. 3 depicts a LIDAR system 300 with a rotating mirror according toembodiments of the present document. LIDAR system 300 employs a singlelaser emitter/detector combined with a rotating mirror to effectivelyscan across a plane. Distance measurements performed by such a systemare effectively two-dimensional (i.e., planar), and the captureddistance points are rendered as a 2-D (i.e., single plane) point cloud.In some embodiments, but without limitations, rotating mirrors arerotated at very fast speeds e.g., thousands of revolutions per minute. Arotating mirror may also be referred to as a spinning mirror.

LIDAR system 300 comprises laser electronics 302, which comprises asingle light emitter and light detector. The emitted laser signal 301may be directed to a fixed mirror 304, which reflects the emitted lasersignal 301 to rotating mirror 306. As rotating mirror 306 “rotates”, theemitted laser signal 301 may reflect off object 308 in its propagationpath. The reflected signal 303 may be coupled to the detector in laserelectronics 302 via the rotating mirror 306 and fixed mirror 304.

As previously noted, time of flight or TOF is the method a LIDAR systemuses to map the environment and provides a viable and proven techniqueused for detecting target objects. Simultaneously, as the lasers fire,firmware within a LIDAR system may be analyzing and measuring thereceived data. The optical receiving lens within the LIDAR system actslike a telescope gathering fragments of light photons returning from theenvironment. The more lasers employed in a system, the more theinformation about the environment may be gathered. Single laser LIDARsystems may be at a disadvantage compared with systems with multiplelasers because fewer photons may be retrieved, thus less information maybe acquired. Some embodiments, but without limitation, of LIDAR systemshave been implemented with 8, 16, 32 and 64 lasers. Also, some LIDARembodiments, but without limitation, may have a vertical field of view(FOV) of 30-40° with laser beam spacing as tight as 0.3° and may haverotational speeds of 5-20 rotations per second.

The rotating mirror functionality may also be implemented with a solidstate technology such as MEMS.

B. Avalanche Photodiodes (APDs) in Multi-Return Light Signal Detectors

As discussed relative to FIG. 2, with a LIDAR system, one laser fire mayhit multiple objects with a different distance in one line, causingmultiple return signals to be received. Detecting multiple return lightsignals in these environments may be extremely challenging for a LIDARsystem especially when an avalanche photodiode (APD) of the LIDAR systembecomes saturated resulting in blinding spot and is unable to detect apeak in a multi-return signal. As used herein, a “peak” is equivalent toa “pulse” of a multi-return signal.

A photodiode is a semiconductor device that converts light into anelectrical current. The current is generated when photons are absorbedin the photodiode. A small amount of current may also be produced whenno light is present. FIG. 4A graphically illustrates the current-voltage(IV) 400 characteristics of a photodiode according to embodiments of thepresent document. When used in zero bias or photovoltaic mode, the flowof photocurrent out of the device is restricted and a voltage builds up.This mode exploits the photovoltaic effect, which is the basis for solarcells. The voltage Vd denotes the voltage that is typically consideredan “on” state for the diode.

Of interest for embodiments of the present document is the operation inthe photodiode mode, where the photodiode operates with a reverse bias.Per FIG. 4A, as the reverse bias voltage increases, the negativecurrent, i, increases in an approximate linear manner until a breakdownvoltage Vbr occurs. After breakdown, the negative current, i, maysignificantly increase as the photodiode saturates. The photodiode maythen enter a reverse bias recovery mode. During the reverse biasrecovery mode the photodiode may be insensitive to light; hence, theremay be a blinding spot in the detection process.

Generally, the photodiode of a LIDAR sensor is an APD. Avalanchephotodiodes are photodiodes with a structure optimized for operatingwith high reverse bias, approaching the reverse breakdown voltage. Thisstructure allows each photo-generated carrier to be multiplied byavalanche breakdown, resulting in internal gain within the photodiode,which increases the effective responsivity of the device.

As previously noted, when the APD is in a reverse bias recovery mode,the photodiode may be insensitive to light. In this case, LIDAR systemlight detection may be prevented until the photodiode recovers to areverse bias mode of operation. For example, laser-based night visionsystems may not overcome the blinding effects associated with highlyreflective objects. Many signs have highly reflective surfaces forreflection of incandescent light, such as that emitted from vehicleheadlamps, for direct viewing ease by a vehicle operator. The signs areoften covered with retro-reflective paint that can reflect a largeamount of light and cause image saturation. A saturated image may begenerally unclear and unreadable. Large flat surfaces, such as ontrucks, buses, and vans, can also cause image saturation. When a brightlight is close to a reflector, the return signal to the light detectormay saturate the APD, causing a blinding spot. Detecting blinding spotsmay be especially important when detecting translucent objects, e.g.,glass kiosks at street corners.

In some embodiments, but without limitation, recovery time may beseveral nanoseconds, for example, but without limitation, 2-6nanoseconds, which may cause a blinding spot of a few meters. FIG. 4Bgraphically illustrates the size on a blinding spot 450 according toembodiments of the present document. Specifically, FIG. 4B indicates theblind spot size in meters relative to the reverse recover time inseconds.

C. Mitigate Blinding Spots in APDs

FIG. 5 graphically illustrates a detected multi-return light signal 500comprising a blinding spot according to embodiments of the presentdocument. The light detection system utilized in the detection processmay be a LIDAR system and the light detection system may performdetection with a single APD. Multi-return light signal 500 comprises asequence of pulses and a blinding spot. As discussed, when a brightlight is close to a reflector, the return signal to the light detectormay saturate the APD, causing a blinding spot. This situation maycompromise the accuracy of the LIDAR system, which may not be resolvedvia calibration. For example, a laser beam may be fired and reflectedoff several reflectors. As illustrated in FIG. 5, the multi-return lightsignal 500 comprises a sequence of three peak signals, as indicated byReflector A, Reflector B and Reflector C. The magnitude of the peaksignals may indicate distance and reflector information. FIG. 5 alsocomprises a blinding spot which may have been caused because a brightlight may have had a close proximity to reflectors, causing saturationof the APD. A fourth peak may have been positioned immediately afterReflector C, but was not detected by the LIDAR system because of theblinding spot. Effectively, the fourth peak was “hidden peak”. In someembodiments, the peak of Reflector C may overlap with the fourth peak.FIG. 5 illustrates performance challenges when decoding subsequent lightpulses in the multi-return light signal 500 when a light detectorutilizes a single APD for the decoding.

Embodiments of the present document propose the use of redundant APDs ina light detection system to improve the accuracy of detection. Forexample, there may be one redundant APD to support every simultaneouslaser firing group. Current LIDAR systems may include multiple APDs witha firing control function that enables one APD at a time to performdetection. One embodiment of the present documents would configure oneredundant APD to support the multiple APDs.

In implementing the redundant APD, space diversity may be utilized tominimize the probability of blinding. Space multiplexing may beimplemented by positioning the redundant APD off the main optical plane,such that the redundant APD may receive less power than a primary APDwhich is positioned on the main optical plane. The primary APDs are“sensitive” APDs inasmuch as they may be positioned on the main focalplane so they are not attenuated and their operation is not restricted.Hence, the optical separation between the sensitive APDs and theredundant APD may allow for attenuating the received optical power inthe redundant APD; thus the term, “attenuated redundant APD”. Anattenuated input may ensure that the attenuated redundant APD may notsaturate when the sensitive APD becomes saturated. The “attenuatedredundant APD” may be referred to as a secondary APD and the “sensitiveAPD” may be referred to as a primary APD.

Additionally, an embodiment of the present documents may improve thedetection performance with the inclusion of time diversity. Timediversity may be achieved by delaying the bias signal to the redundantAPD relative to the bias signal of the sensitive APD.

1. Light Detector with a Redundant APD

FIG. 6 depicts a light detector 600 with a redundant APD according toembodiments of the present document. Light detector 600 may be utilizedin a LIDAR system. Light detector 600 incorporates space diversity andtime diversity functions and comprises four primary (sensitive) APDs andone secondary (redundant) APD. The secondary APD may operate with anyone of the primary APDs. As described herein, light detector 600 mayoperates on a static or dynamic basis. One embodiment of staticoperation, the operation of the secondary APD and primary APDs may bepre-defined and may be independent of the characteristics ofmulti-return light signals.

A multi-return light signal may be received by a bank of primary APDsincluding sensitive APDs 604 a, 604 b, 604 c and 604 d, or sensitive APDbank 604. Sensitive APDs 604 a, 604 b, 604 c and 604 d may be activatedby a controller based on a laser firing sequence. The controller may beAPD range gate control 610, which is coupled to sensitive APDs 604 a,604 b, 604 c and 604 d via signals 603 a, 603 b, 603 c and 603 d,respectively. APD range gate control 610 may also be coupled to delay608. One skilled in the art will recognize that in other embodiments, abank of sensitive APDs may comprise n number of APDs and may not belimited to four APDs. In some embodiments, the number n of primary APDsmay vary between 16 and 128.

In one embodiment, attenuated redundant APD 606 may operate as aredundant APD to sensitive APD 604 a. APD range gate control 610activates sensitive APD 604 a causing sensitive 604 a to receivedmulti-return light signal 602. The characteristics of multi-return lightsignal 602 may cause a blinding spot for sensitive APD 604 a during thedetection process. Simultaneously, APD range gate control 610 activatesdelay 608, causing attenuated redundant APD 606 to be activated with atime delay relative to the activation of sensitive APD 604 a. Thisdelayed bias gate for attenuated redundant APD 606 provides timediversity relative to sensitive APD 604 a via delay 608. As the lightdetector 600 sequences through laser firing control, other APDs insensitive APD bank 604 are selected, e.g. sensitive APDs 604 b, 604 cand 604 d. As each of these other sensitive APDs is activated,attenuated redundant APD 606 operates in a redundant manner to supportthe selected sensitive APD.

Attenuated redundant APD 606 may be activated by APD range gate control610 with time diversity relative to any of the APDs in the sensitive APDbank 604. Delay 608 may be turned on to allow for a time diversityfactor between sensitive APD bank 604 and attenuated redundant APD 606.The delay step size may be a fraction of the laser width pulse. Timediversity may improve the accuracy of detection of multi-return lightsignals, as will be discussed relative to FIGS. 7A, 7B, 7C.

Space diversity may be implemented as follows. First, each of the APDsin the sensitive APD bank 604 may be located at a different opticalplane from one another. Attenuated redundant APD 606 may be located at adifferent optical plane than the APDs in the sensitive APDs bank 604.The optical separation between the APDs in the sensitive APDs bank 604and the redundant APD may allow for attenuating the received opticalpower in the redundant APD; hence the term, “attenuated redundant APD606”. Space diversity may be achieved via use of semi-transparentmirrors. For example, but without limitations, current mirrors may have2% transmissive, so one can put the redundant APDs behind the currentmirror, which may be a different optical plane.

The sensitive APD bank 604 may operate with attenuated redundant APD 606to mitigate the possibility of APD blinding. Sensitive APD 604 a may beactivated and may detect a sequence of return signals. With timediversity (a delay) and space diversity, attenuated redundant APD 606may be activated to support the detection of the sequence of returnsignals in light detector 600. Attenuated redundant APD 606 may detect ahidden pulse when sensitive APD 604 a is saturated and has a blindingspot, which may negatively impact the detection capability of sensitiveAPD 604 a.

The output of attenuated redundant APD 606 may be coupled to low noisecurrent amplifier 612 to amplify its current. A controller activatesgain control 614 utilizing inverting gain ratio control to manage theresulting outputs from attenuated redundant APD 606 and sensitive APD604 a. Each resulting output may have a different gain based on theinverting gain ratio control. The resulting outputs are coupled tocombiner 616, which implements MIMO processing with maximum gain ratiocombining maximum gain ratio combining. The output of combiner 616 iscoupled to trans-impedance amplifier (TIA) 618. The output oftrans-impedance amplifier 618 is coupled to diversity enhanced opticaldetector 620 that outputs the detected multi-return signal 622.

Combiner 616 may have undesirable noise due to the two parallel paths:one from low noise current amplifier 612 (based on attenuated redundantAPD 606) and one from sensitive APD 604 a. Dynamic weighting of theparallel paths may mitigate the impact of noise. For example, if thesensitive APD 604 a current is below a threshold, the current based onattenuated redundant APD 606 may be de-weighted. If the sensitive APD604 a current is below a noise floor, the sensitive APD 604 a currentmay be de-weighted. In a high noise environment, combiner 616 stopscombining, and only monitors its inputs.

FIGS. 7A, 7B and 7C graphically illustrate waveforms 700, 720 and 740for the operation of light detector 600 of FIG. 6 with a redundant APDaccording to embodiments of the present document. Specifically, FIGS.7A, 7B and 7C graphically illustrate waveforms resulting from sensitiveAPD 604 a and attenuated redundant APD 606. FIG. 7A illustrates twopulses of multi-return light signal 602 where first pulse is in closeproximity to the second pulse. The pulses are represented as idealrectangular pulses.

FIG. 7B illustrates a response or output of sensitive APD 604 a and fromattenuated redundant APD 606. During the generation of this output,sensitive APD 604 a may become saturated resulting in a blinding spot(see blind zone). In other words, FIG. 7B illustrates the close inbright reflector saturating the sensitive APD 604 a, i.e., the primaryAPD. During recovery from saturation, sensitive APD 604 a may be unableto detect the second pulse. Typical saturation recovery may last forseveral nanoseconds (ns). Therefore, at ˜30 cm/ns, 6 ns may result in ablinding spot of 2 meters.

FIG. 7B also illustrates the response or output of attenuated redundantAPD 606 (i.e., response redundant APD), which is located off theprinciple optical axis of sensitive APD 604 a. Therefore the “redundantAPD” is attenuated. Per FIG. 7B, the magnitude of the “response ofsensitive detector” is greater than the magnitude of the “responseredundant APD”.

The output of attenuated redundant APD 606 may be electrically amplifiedby low noise current amplifier 612, resulting in waveforms 740 of FIG.7C. Waveform 740 shows the result of MIMO processing with Maximum GainRatio Combining to capture two events in close proximity.

Waveforms 740 comprise the response of sensitive APD 604 a (the firstpulse) and the amplified output of attenuated redundant APD 606 (thesecond pulse). Because of the amplification of low noise currentamplifier 612, the pulse (second pulse) detected by the attenuatedredundant APD 606 is now larger that the pulse (first pulse) detected bysensitive APD 604 a. Waveform 740 may be decoded by a diversity receiversince waveform 740 includes close rising edges.

2. Method of Light Detection with a Redundant APD

A method of detecting a multi-return light signal by a light detectionand ranging system, e.g., a LIDAR system is described. FIG. 8 depicts aflowchart 800 for detecting multi-return light signals utilizing a lightdetector with a redundant APD according to embodiments of the presentdocument. More specifically, FIG. 8 describes a method of detecting ahidden pulse in a multi-return light signal where the first pulse causessaturation in the primary APD, resulting in a blinding spot. (See FIG.7B.)

In the following steps, references are made to some elements of lightdetector 600. Also, in the following steps, the primary APD may be oneof sensitive APD 604 abcd and the secondary APD may be attenuatedredundant APD 606. The steps of the method comprise:

Receiving a multi-return light (MRL) signal comprising pulses that mayhave close proximity to one another. The MRL signal may comprise ahidden pulse resulting from a close in bright reflector that may causesaturation of a primary APD (high gain detector) in light detector 600.(step 802)

Activating APD range gate control 610 to generate a bias signal. Thisaction determines activation sequence of primary APDs and secondaryAPDs. Gain control 610 is activated. (step 804)

Receiving at a selected primary APD (high gain detector) the bias signaland the MRL signal. The primary APD may be selected from sensitive APDbank 604 based on firing control. Also, each APD in the sensitive APDbank 604 may be positioned at a different optical plane. The primary APDgenerates a trigger for the secondary APD. (step 806)

Receiving at a secondary APD the MRL signal and a delayed bias signal,wherein the bias signal is delayed by delay 608. The delayed bias signalmay cause the secondary APD to detect in a delayed time window relativeto the primary APD. The secondary (redundant) APD may be in a differentoptical plane than the primary APD causing the signal emitted from thesecondary (redundant) APD to be “attenuated” relative to the signalemitted from the primary (sensitive) APD. (step 808)

Activating gain control 614 utilizing inverting gain ratio control tomanage the resulting outputs from the secondary APD and the primary APD.(step 812)

Amplifying the output of the secondary APD with low noise currentamplifier 612 based on gain control 614 of step 812. (step 810)

Combining the resulting signals from the primary APD and the secondaryAPD utilizing MIMO processing with Maximum Gain Ratio Combining tocapture two pulses (events) in close proximity. (step 814)

Amplifying the results of step 814 with a trans-impedance amplifier.(step 816)

Detecting and outputting the multi-return signal including one or morehidden pulses with a diversity enhanced optical detector 620. (step 818)

D. Embodiments for Redundancy

As previously discussed, the performance of light detection of amulti-return light signal may be improved with the inclusions of asecondary APD that operates redundantly to a primary APD. Theperformance may be further improved with the inclusion of timediversity, e.g., where the bias signal to the secondary APD is delayedrelative to the primary APD. The performance may be further improvedwith the inclusion of space diversity of the optical planes of theprimary APD and the secondary APD. With space diversity, the output ofthe secondary APD may to attenuated, which may minimizes the possibilityof the secondary APD saturating and entering a reverse bias recoveryperiod. This may allow the secondary APD to detect hidden pulses.

Various configurations for the secondary and primary APDs may havefurther performance improvements. Example embodiments include, butwithout limitations, 1 secondary APD for 1 primary APD, 1 secondary APDfor n primary APDs and m secondary APDs for n primary APDs. In otherwords, multiple redundant APDs may be utilized with differentcombinations of primary APDs. The secondary and primary APDs may operatein a static environment or in a dynamic environment. As describedherein, light detector 600 may operates on a static basis. For a staticenvironment, the operation of the redundant APDs and primary APDs may bepre-defined and may be independent of the characteristics of themulti-return light signals.

Dynamic solutions may be based on signal processing information of themulti-return light signals. Possible dynamic embodiments may include,but without limitations: 1) changing firing control order of primaryAPDs. This embodiment may include activating two or more primary APDs ata point in time; 2) dynamically adjusting the redundancy alignment ofmultiple secondary APDs and multiple primary APDs based on thepositioning of the selected APDs on the optical focal plan; and 3)dynamically adjusting the delay bias signal coupled to the secondaryAPDs.

E. Summary

Embodiments of the present documents disclose systems and methods formitigating APD blinding. A system may comprise a primary avalanchephotodiode (APD) operable to receive and detect a multi-return lightsignal when activated by a first bias signal, wherein, the multi-returnlight signal comprises two or more light pulses; a secondary APDoperable to receive and detect the multi-return light signal whenactivated by a second bias signal; a delay function that generates thesecond bias signal by adding a delay to the first bias signal; and acombiner operable to combine the multi-return light signal detected bythe primary APD and the multi-return light signal detected by thesecondary APD, wherein, if the primary APD saturates when detecting themulti-return light signal and is unable to detect a subsequent pulse,the secondary APD decodes the subsequent pulse. A method comprisesreceiving a multi-return light signal at a primary APD, wherein themulti-return light signal comprises a sequence of pulses that cause theprimary APD to saturate and generate a detection blinding spot;receiving the multi-return light signal at a secondary APD, wherein thesecondary APD operates redundantly to the primary APD; and detecting, bythe secondary APD, pulses in the multi-return light signal that arehidden in the detection blinding spot of the primary APD and notdetected by the primary APD. A system comprises two or more primaryavalanche photodiodes (APDs), each operable to detect a multi-returnlight signal when activated by a first bias signal, wherein themulti-return light signal comprise two or more pulses; two or moresecondary APDs, each operable to detect the multi-return light signalwhen activated by a second bias signal, wherein each of the two or moresecondary APDs are operable to operate redundantly with each of the twoor more primary APDS to perform the detection of the multi-return lightsignal; and a controller operable to select one of the two or moresecondary APDs and one of the two or more primary APDs for detection ofthe multi-return light signal

F. System Embodiments

In embodiments, aspects of the present patent document may be directedto or implemented on information handling systems/computing systems. Forpurposes of this disclosure, a computing system may include anyinstrumentality or aggregate of instrumentalities operable to compute,calculate, determine, classify, process, transmit, receive, retrieve,originate, route, switch, store, display, communicate, manifest, detect,record, reproduce, handle, or utilize any form of information,intelligence, or data for business, scientific, control, or otherpurposes. For example, a computing system may be an optical measuringsystem such as a LIDAR system that uses time of flight to map objectswithin its environment. The computing system may include random accessmemory (RAM), one or more processing resources such as a centralprocessing unit (CPU) or hardware or software control logic, ROM, and/orother types of memory. Additional components of the computing system mayinclude one or more network or wireless ports for communicating withexternal devices as well as various input and output (I/O) devices, suchas a keyboard, a mouse, touchscreen and/or a video display. Thecomputing system may also include one or more buses operable to transmitcommunications between the various hardware components.

FIG. 9 depicts a simplified block diagram of a computingdevice/information handling system (or computing system) according toembodiments of the present document. It will be understood that thefunctionalities shown for system 900 may operate to support variousembodiments of an information handling system—although it shall beunderstood that an information handling system may be differentlyconfigured and include different components.

As illustrated in FIG. 9, system 900 includes one or more centralprocessing units (CPU) 901 that provides computing resources andcontrols the computer. CPU 901 may be implemented with a microprocessoror the like, and may also include one or more graphics processing units(GPU) 917 and/or a floating point coprocessor for mathematicalcomputations. System 900 may also include a system memory 902, which maybe in the form of random-access memory (RAM), read-only memory (ROM), orboth.

A number of controllers and peripheral devices may also be provided, asshown in FIG. 9. An input controller 903 represents an interface tovarious input device(s) 904, such as a keyboard, mouse, or stylus. Theremay also be a wireless controller 905, which communicates with awireless device 906. System 900 may also include a storage controller907 for interfacing with one or more storage devices 908 each of whichincludes a storage medium such as flash memory, or an optical mediumthat might be used to record programs of instructions for operatingsystems, utilities, and applications, which may include embodiments ofprograms that implement various aspects of the present invention.Storage device(s) 908 may also be used to store processed data or datato be processed in accordance with the invention. System 900 may alsoinclude a display controller 909 for providing an interface to a displaydevice 911. The computing system 900 may also include an automotivesignal controller 912 for communicating with an automotive system 913. Acommunications controller 914 may interface with one or morecommunication devices 915, which enables system 900 to connect to remotedevices through any of a variety of networks including an automotivenetwork, the Internet, a cloud resource (e.g., an Ethernet cloud, anFiber Channel over Ethernet (FCoE)/Data Center Bridging (DCB) cloud,etc.), a local area network (LAN), a wide area network (WAN), a storagearea network (SAN) or through any suitable electromagnetic carriersignals including infrared signals.

In the illustrated system, all major system components may connect to abus 916, which may represent more than one physical bus. However,various system components may or may not be in physical proximity to oneanother. For example, input data and/or output data may be remotelytransmitted from one physical location to another. In addition, programsthat implement various aspects of this invention may be accessed from aremote location (e.g., a server) over a network. Such data and/orprograms may be conveyed through any of a variety of machine-readablemedium including, but are not limited to: magnetic media such as harddisks, floppy disks, and magnetic tape; optical media such as CD-ROMsand holographic devices; magneto-optical media; and hardware devicesthat are specially configured to store or to store and execute programcode, such as application specific integrated circuits (ASICs),programmable logic devices (PLDs), flash memory devices, and ROM and RAMdevices.

Embodiments of the present invention may be encoded upon one or morenon-transitory computer-readable media with instructions for one or moreprocessors or processing units to cause steps to be performed. It shallbe noted that the one or more non-transitory computer-readable mediashall include volatile and non-volatile memory. It shall be noted thatalternative implementations are possible, including a hardwareimplementation or a software/hardware implementation.Hardware-implemented functions may be realized using ASIC(s),programmable arrays, digital signal processing circuitry, or the like.Accordingly, the “means” terms in any claims are intended to cover bothsoftware and hardware implementations. Similarly, the term“computer-readable medium or media” as used herein includes softwareand/or hardware having a program of instructions embodied thereon, or acombination thereof. With these implementation alternatives in mind, itis to be understood that the figures and accompanying descriptionprovide the functional information one skilled in the art would requireto write program code (i.e., software) and/or to fabricate circuits(i.e., hardware) to perform the processing required.

It shall be noted that embodiments of the present invention may furtherrelate to computer products with a non-transitory, tangiblecomputer-readable medium that have computer code thereon for performingvarious computer-implemented operations. The media and computer code maybe those specially designed and constructed for the purposes of thepresent invention, or they may be of the kind known or available tothose having skill in the relevant arts. Examples of tangiblecomputer-readable media include, but are not limited to: magnetic mediasuch as hard disks, floppy disks, and magnetic tape; optical media suchas CD-ROMs and holographic devices; magneto-optical media; and hardwaredevices that are specially configured to store or to store and executeprogram code, such as application specific integrated circuits (ASICs),programmable logic devices (PLDs), flash memory devices, and ROM and RAMdevices. Examples of computer code include machine code, such asproduced by a compiler, and files containing higher level code that areexecuted by a computer using an interpreter. Embodiments of the presentinvention may be implemented in whole or in part as machine-executableinstructions that may be in program modules that are executed by aprocessing device. Examples of program modules include libraries,programs, routines, objects, components, and data structures. Indistributed computing environments, program modules may be physicallylocated in settings that are local, remote, or both.

One skilled in the art will recognize no computing system or programminglanguage is critical to the practice of the present invention. Oneskilled in the art will also recognize that a number of the elementsdescribed above may be physically and/or functionally separated intosub-modules or combined together.

It will be appreciated to those skilled in the art that the precedingexamples and embodiments are exemplary and not limiting to the scope ofthe present disclosure. It is intended that all permutations,enhancements, equivalents, combinations, and improvements thereto thatare apparent to those skilled in the art upon a reading of thespecification and a study of the drawings are included within the truespirit and scope of the present disclosure. It shall also be noted thatelements of any claims may be arranged differently including havingmultiple dependencies, configurations, and combinations.

What is claimed is:
 1. A system comprising: a primary avalanchephotodiode (APD) operable to receive and detect a multi-return lightsignal when activated by a first bias signal, the multi-return lightsignal comprises two or more light pulses; a secondary APD operable toreceive and detect the multi-return light signal when activated by asecond bias signal; a delay function that generates the second biassignal by adding a delay to the first bias signal; and a combineroperable to combine the multi-return light signal detected by theprimary APD and the multi-return light signal detected by the secondaryAPD, wherein, if the primary APD saturates when detecting themulti-return light signal, the secondary APD decodes the subsequentpulse.
 2. The system of claim 1 further comprising a range gate controloperable to control the delay function.
 3. The system of claim 1,wherein the secondary APD is attenuated relative to the primary APD inorder to prevent saturation of the secondary APD under conditions whenthe primary APD saturates.
 4. The system of claim 3, wherein thesecondary APD is attenuated relative to the primary APD by positioningthe secondary APD on a different optical plane than the primary APDcausing the secondary APD to receive less power than the primary APD. 5.The system of claim 1 further comprising a current amplifier operable toamplify output current of the secondary APD.
 6. The system of claim 5further comprising a gain controller operable to control the currentamplifier via inverting gain ratio control based on the output currentof the secondary APD and an output current of the primary APD.
 7. Thesystem of claim 1 further comprising a diversity enhanced opticaldetector coupled to an output of the combiner and operable to generate adetected multi-return signal.
 8. The system of claim 1, furthercomprising two or more primary APDs, wherein the secondary APD providesredundant support for the two or more primary APDs based on a firingcontrol sequence for the primary APDs.
 9. The system of claim 1, furthercomprising two or more primary APDs and two or more secondary APDs. 10.The system of claim 9, wherein selecting one of the two or more primaryAPDs, and one of the two or more secondary APD in order to detect themulti-return light signal.
 11. The system of claim 1, wherein, thecombiner implements MIMO processing with maximum gain ratio combining.12. A method comprising: receiving a multi-return light signal at aprimary APD, wherein the multi-return light signal comprises a sequenceof pulses that cause the primary APD to saturate and generate adetection blinding spot; receiving the multi-return light signal at asecondary APD, wherein the secondary APD operates redundantly to theprimary APD; and detecting, by the secondary APD, pulses in themulti-return light signal that are hidden in the detection blinding spotof the primary APD and not detected by the primary APD.
 13. The methodof claim 12 further comprising: attenuating received optical power inthe secondary APD by obtaining optical separation between the secondaryAPD and the primary APD.
 14. The method of claim 13, wherein, if theprimary APD is saturated by the multi-return light signal, the secondaryAPD avoids saturation because of its attenuated power level.
 15. Themethod of claim 12, wherein detection of the multi-return light signalat the primary APD is activated by a first bias signal and detection ofthe multi-return light signal at the secondary APD is activated by asecond bias signal, wherein the second bias signal equal the first biassignal plus a delay step.
 16. The method of claim 15, wherein the delaystep is a fraction of laser width pulses of the multi-return lightsignal.
 17. A system comprising: two or more primary avalanchephotodiodes (APDs), each operable to detect a multi-return light signalwhen activated by a first bias signal, wherein the multi-return lightsignal comprise two or more pulses; two or more secondary APDs, eachoperable to detect the multi-return light signal when activated by asecond bias signal, wherein each of the two or more secondary APDs areoperable to operate redundantly with each of the two or more primaryAPDS to perform the detection of the multi-return light signal; and acontroller operable to select one of the two or more secondary APDs andone of the two or more primary APDs for detection of the multi-returnlight signal.
 18. The system as in claim 17, wherein a basis forselections of primary and secondary APDs is pre-defined.
 19. The systemas in claim 17, wherein primary and secondary APDs are dynamicallyselected based on signal processing information of the multi-returnlight signal.
 20. The system as in claim 19, wherein the dynamicselection changes a firing order of the primary APDs.
 21. The system ofclaim 19, wherein the dynamic selection adjusts the second bias signalrelative to the first bias signal.
 22. The system of claim 19, whereinthe dynamic selection is based on respective positions on focal plane ofthe primary and secondary APDs.
 23. The system of claim 17, wherein theselected secondary APD is positioned off a main optical focal plane ofthe selected primary APD in order to attenuate the selected secondaryAPD relative to the selected primary APD.